The present invention relates to air conditioners for use in automotive vehicles, and more particularly to improvements in or to the heater unit of such air conditioner, for heating refrigerated air supplied from the cooling unit and, when required, mixing refrigerated air and hot air to control the discharge air temperature.
A conventional heater unit of this kind is constructed such that a temperature adjusting damper is arranged in an air inlet passage connected to the outlet of a cooling unit, at its downstream end and is pivotable to allow part of refrigerated air supplied from the cooling unit to the air inlet passage to pass through a heater core provided therein, while allowing the remainder of the refrigerated air to bypass the heater core, and the resulting hot air and the bypassing air are mixed together at a zone downstream of the heater core so as to obtain a desired discharge air temperature. When this heater unit is in maximum cooling mode, the temperature adjusting damper is in a position to close the inlet of the heater core where all the refrigerated air supplied to the air inlet passage is guided directly to the discharging air passage, bypassing the heater unit. However, part of this bypassing air can be guided to the heater core through a hot air passage extending between the outlet of the heater core and the discharging air passage to be heated by the heater core, so that the resulting hot air is discharged into the passenger compartment of a vehicle associated with the heater unit, together with the remainder of the bypassing air, thus resulting in insufficient cooling inside the compartment.
To eliminate the above disadvantage, the conventional heater unit is usually provided with a water valve which is adapted to temporarily interrupt the supply of heating medium or hot water to the heater core when the heater unit is in maximum cooling mode. However, this valve is expensive, leading to a high manufacturing cost.
A low-cost type heater unit has therefore been proposed according to Japanese Utility Model Publication No. 54-27713, which includes an auxiliary damper which is used in place of the above-mentioned water valve and which is arranged opposite the outlet of the heater core for pivoting in unison with the temperature adjusting damper to selectively open and close the same outlet to thereby prevent part of the bypassing air delivered to the discharging air passage from being guided to the outlet of the heater core through the hot air passage to be heated directly by the heater core. However, according to this proposed structure, the auxiliary damper is heated by the heat of the heater core to eventually heat the bypassing air. Further, the auxiliary damper needs to be designed as large in size as the area of the outlet of the heater core, which requires providing a large space in front of the outlet of the heater core, for accomodating the auxiliary damper in a pivotable fashion. Therefore, the proposed heater unit is not suitable for use in an automotive vehicle in general which has a limited space for installment of the heater unit.